Foamed pet packaging

ABSTRACT

This invention provides packages and containers produced by a solid state method for the manufacture of foamed polymeric material. The packages are suitable for pre-cooking or sterilization, insulated transport, cooking vessel, reheating, and storage of food. The gas impregnated thermoforming (GIT) process includes interleaving an article of raw polymeric material with a gas channeling means; exposing the article to a non-reacting gas at elevated pressure to achieve a desired concentration of gas within the polymer, thereby forming a partially gas-saturated article, separating it from the gas channeling means, then decompressing, foaming and forming it at a temperature below the material&#39;s melt temperature; and finally trimming it to produce a finished foamed polymeric material and recycleable scrap solid state process foamed polymer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional application No.60/471,477, filed May 17, 2003, titled THERMOFORMED FOAMED THERMOPLASTICPACKAGING.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to special receptacles or packages adapted tocontain food and to receptacles used to cook food by means of a heatsource. It also relates to packaging suitable for other, non-foodpurposes, when ease and economy of manufacture, thermal insulation,shape stability at high service or operating temperature, and heat andimpact resistance are significant factors.

2. Description of the Related Art

Products in which food is packaged, prepared and served are ubiquitousin modem life. Ranging from preparation, pre-cooking, presentation,serving, cooking, storage and reheating, uses to which such products areput vary widely. Further, ranging from single-use disposable packaging,through inexpensive limited multi-use products, through durable goods,such containers vary widely in cost and durability. Manufactured frommaterials including laminated cardboard, thermoformed polymer, foamedpolymer and injection molded polymer, such products are also of widelyvarying composition.

Examining uses for such products in more detail, in the United States inparticular, significant industrial activity is devoted to producingsingle use, disposable packaging for serving food in the restaurantindustry. Polystyrene foam boxes have been used for some time for foodpackaging as in restaurant take-out boxes. Laminated cardboardcontainers are also used extensively for packaging restaurant take-outfood. The pizza restaurant industry is dependent to a large degree onthe utility of cardboard pizza take-out boxes.

With the increasing use of prepared frozen and heat-and-serve foods,demand has multiplied for single use or limited multi-use packaging inwhich food is prepared, precooked and marketed by producers and thencooked and served by consumers. While frozen dinners, packaged and soldas such for later cooking by the consumer, such as claimed in U.S. Pat.No. 3,244,537, have long been a mainstay of the American table, packagedprepared meals stored on the shelf at room temperature for purchase andcooking by the consumer, such as described and claimed in U.S. Pat. No.5,904,946 are becoming increasingly common as well.

More expensive, longer-lived plastic containers for food storage, suchas depicted and claimed in U.S. design Pat. No. D277,632 or thewell-known Tupperware® are useful and popular items in most Americankitchens. Further, consumers have welcomed the recent availability ofinexpensive limited multi-use containers for dishware, storage andcooking, such as Ziploc® brand storage containers with Snap 'n Seallids, as depicted and claimed in U.S. design Pat. No. D476,861.

Despite the ubiquity and variety of such products, the prior art issubject to significant limitations. Few materials or packages evenapproach suitability for all the uses to which food packaging issubject. Some prior art packages, which serve their limited uses well,are too expensive for other uses. Others are completely incapable of useoutside of their limited area of applicability. Further, there are someuses that are desirable for food packaging that are not met at all bythe prior art. In addition, much prior art food packaging is recycledwith difficulty, if at all, and therefore is environmentally costly.

As is well known to those in the art, polystyrene foam in the prior artis in two basic forms: thermoformed extruded sheet (ESF) and expandedbead foam (EBF).

ESF foamed polymers are created by foaming extrusion, which entailsproducing or forcing a non-reactive foaming gas into a molten polymermixture or alternately creating gas with chemical reactions within themolten polymer, thereby forming bubbles in the melt. The foamed meltedmaterial is extruded as a sheet of plastic containing fine bubblesforming microcells and is then allowed to cool. For forming ESF objects,the ESF material is subsequently cured for a period of time to allow gaspressures in the microcells to become optimal for forming, after whichthe material is thermoformed.

Boxes made from ESF Polystyrene foam are adequate for transporting foodand provide excellent thermal insulation, enabling consumers to keeprestaurant food warm from purchase until later consumption. However,polystyrene foam in general has little tensile strength and containerstear easily. Further, because it has little heat resistance, polystyrenefoam is unsuitable for more than brief warming in a microwave oven andis wholly unsuited to heating in a conventional oven. In addition,polystyrene foam containers generally do not seal well and so areunsatisfactory for extensive storage of food. Lastly, the geometry ofobjects that can be thermoformed with prior art ESF is quite limited,restricting height to depth ratios to considerably less than 1:1, andwall angles to no less than about 40 deg from vertical.

EBF foam is made by saturating polystyrene pellets with blowing agent(typically a hydrocarbon gas such as butane or pentane), followed byblowing steam through the pellets, which penetrates the beads and actsas a secondary blowing agent while it heats the beads sufficiently tocause foaming. In forming objects, the foamed beads are then transferredto a molding machine where they are compressed and further steamedcausing the beads to fuse to make the desired object, such as apolystyrene cup.

EBF foamed objects may be formed with height to depth ratios over 1:1and wall angles approaching vertical. They are produced in net shape,requiring no trimming after manufacture, and, like all polystyrene foamproducts, they provide excellent thermal insulation. However, EBF foamedproducts have the same drawbacks of polystyrene foam products generally,and, in addition, EBF foamed products have even less tensile strengthand durability than ESF polystyrene foamed products.

Regardless of method of manufacture, prior art foamed packaging suffersfrom a number of additional significant drawbacks. Polystyrene foamedmaterials can't withstand high temperatures and therefore are notmicrowaveable or ovenable above, about the boiling point of water. Inaddition, such foam containers usually lack quality, tight fitting lids,reducing their utility for food storage. Finally, all prior artpolystyrene foamed materials, regardless of method of manufacture, arenon-biodegradable and have little value for recycling, and therefore areenvironmentally costly.

While coated cardboard containers may be microwaved and, in fact, ifcomprised of appropriate materials, may be used for limited cooking andreheating in conventional ovens, such containers are unsuitable forextensive cooking or for storage beyond very short term. Further, theinsulation properties of coated cardboard are slight, and clearlyinferior to those of polystyrene foam. Furthermore, because ofnon-degradable, non-recyclable laminations due to the plastic coatingsrequired for significant food contact life, many such containers arescarcely more recyclable than polystyrene foam.

Prior art pizza boxes, generally composed of corrugated cardboard, serveto insulate and transport the food. Most are rectangular in shape andmany are not dimensioned for heating in home microwave ovens, and thecardboard material is unsuitable for use in a conventional oven.Further, prior art pizza boxes are unsuitable for long-term storage,because they do not seal tightly, allowing pizza to become stale, andthe cardboard material decomposes as it absorb oils and liquids fromfood contained therein. While some prior art has employed foamed polymerfor pizza boxes, as in U.S. Pat. No. 4,848,543, such prior art comprisesboxes principally of polystyrene foam. Not only is such foam subject tothe general limitations of polystyrene foam containers noted above, butits low heat resistance makes it unsuitable for receiving pizzaimmediately after cooking.

While polymer containers for frozen and other pre-cooked foods arecommonly microwavable, many such containers are not adaptable forcooking in conventional ovens. Some solid polymer containers, such asthose of highly crystallized PET (CPET) are useable in both microwaveand conventional ovens. Solid polypropylene containers can be heated toabout the temperature of boiling water for sterilization, but cannotwithstand oven cooking temperatures. Foil containers, while almostobsolete, are unusable in microwave ovens. Regardless of suitability formicrowave or oven, all such containers generally provide little if anythermal insulation for foods and are therefore unsuitable formaintaining foods at serving temperature. In addition, such containersusually lack quality, tight fitting lids, reducing their utility forfood storage. Further, both foil and solid polymer containers areconsiderably more costly to produce than foamed polymer containers.

Longer-lived containers of the Tupperware sort provide excellent foodstorage but provide little thermal insulation. Such containers are notheat resistant and so, while they may be used for fast heating inmicrowave ovens, they are unsuitable for longer cooking times and maynot be used in conventional ovens. In addition, such containers costmany times the cost of other containers considered herein. While thenewer, shorter-lived multi-use containers are considerably lessexpensive, they also suffer from shortcomings in insulation capabilityand heat resistance.

Yet a further limitation applicable to much of the prior art processesfor production of food containers is that scrap material from themanufacture of such containers is generally of little value and, infact, may require costly disposal. Accordingly, the configuration ofprior art food containers is often constrained by the need to minimizethe scrap produced in their manufacture, thereby resulting in containersthat are less than optimally shaped for their purpose.

What is needed are food containers suitable for pre-cooking orsterilization, insulated transport, use as a cooking vessel, reheating,and storage of food. What is needed further is an economical way ofproducing such containers at low cost. What is yet further needed is aprocess for producing such containers whereby there is little economicconstraint on container shape. What is yet further needed are suchcontainers that are also environmentally sound.

It has recently been discovered that polymer foam articles may beproduced on an industrial scale by a novel process, gas impregnatedthermoforming (GIT). In U.S. Pat. No. 5,684,055 to Kumar et al.,incorporated herein by reference in its entirety, a roll of polymersheet is provided with a gas channeling means interleaved between thelayers of polymer. The roll is exposed to a non-reacting gas at elevatedpressure for a period of time sufficient to achieve a desiredconcentration of gas within the polymer. The saturated polymer sheet isthen separated from the gas channeling means and bubble nucleation andgrowth is initiated by heating the polymer sheet. After foaming, bubblenucleation and growth is quenched by cooling the foamed polymer sheet.The foamed sheet may then be thermoformed.

As further elaborated in PCT patent application number PCT/US __/______,titled METHOD OF PRODUCING THERMOFORMED ARTICLES FROM GAS IMPREGNATEDPOLYMER, filed contemporaneously herewith and incorporated herein byreference, such process is suitable for foaming with a wide range ofgas/polymer systems comprised of non-reacting gas and amorphous orsemi-crystalline thermoplastic polymer materials, including CO2 withpolyethylene, polyethylene terephthalate (PET), polyvinyl chloride,acrylonitrile butadiene styrene, polycarbonate, and polypropylene, whileN2 may be used with polystyrene.

In U.S. Pat. Nos. 5,223,545 and 5,182,307 to Kumar et al., bothincorporated herein by reference in their entirety, PET is shown to haveits crystallinity levels raised by saturation with high pressure CO2gas. Furthermore it has been shown that the crystallizing gas remains inthe polymer for a time in substantial quantities after foaming andenhances crystallization during thermoforming.

It has been further been discovered that objects made from such foamspossess surprising qualities that render such objects particularlysuited for food packaging applications. Based upon these discoveries, itis an object of this invention to provide food containers suitable forpre-cooking or sterilization, insulated transport, use as a cookingvessel, reheating, and storage of food. It is a further object of thisinvention to provide an economical way of producing such containers atlow cost. It is yet a further object of this invention to provide foodpackaging that is more ecologically sound for more varied applicationsthan is available in the prior art.

BRIEF SUMMARY OF THE INVENTION

The present invention utilizes the gas impregnated thermoforming (GIT)process to manufacture packages and containers of foamed PET withoptional integral skins of variable crystallinity. These containers maybe used to store food at all stages of the cooking process. The packagesare suitable for pre-cooking or sterilization, insulated transport,cooking vessel, reheating, and storage of food. The versatility of thepackage is made possible by the inherent nature of the material. Itinsulates to keep hot food hot and cold food cold. The package isadvantageous over other disposable materials since it contains nosolvent residues or other undesirable chemicals that can spoil thetaste, quality, or safety of the food.

The high temperature resistance of highly crystallized PET, whether juston the surface of containers or extending into the container's interior,makes it possible for the consumer to cook food right in the box withoutfear of melting it. The insulating characteristics of the foam materialenhance maintenance of serving temperature. The cut resistant integralskin makes the box attractive for cutting the food directly thereon. Itis also advantageous to serve the food directly from the container. Thecracking resistance and stability of the material over a widetemperature range make it possible or desirable to refrigerate or freezeunconsumed leftovers directly in the same container. The thermal shapestability of highly crystallized PET at higher temperatures makes itadvantageous to reheat the food in a microwave, convection, orconventional oven directly in the box. Finally, the entire package maybe recycled, owing to the integral nature of the skins with theirinherent chemical similarity to the core foam, lack of flammable gases,and lack of chemical change to the polymer during or required by thefoaming process.

If a plasticizing gas is used for gas impregnation, the plasticity ofthe polymeric material may be greatly enhanced, substantially loweringthe viscosity of the material at a given temperature. The positivepressure remaining in microcells of materials foamed by the solid stategas impregnation process immediately after foaming further greatlyenhances the formability of such materials. Accordingly, for embodimentsthat are plasticized and/or foamed by gas impregnation, it is possibleto thermoform containers of geometries hitherto unattainable.

Because of the substantially 100% recycleability of foam materialscreated according to the present process, round containers, and othershapes that would normally be prohibitive in ESF due to the relativelylarge amount of trim are especially feasible. This allows containers tobe fabricated in shapes more optimized for the application, havingproperties such as improved aesthetics, improved heat retention, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, features and characteristics of the presentinvention, as well as methods, operation and function of relatedelements of structure, and the combination of parts and economies ofdeployment, will become apparent upon consideration of the followingdescription and claims with reference to the accompanying drawings, allof which form a part of this specification, wherein:

FIG. 1 is a cross-sectional view of a foamed thermoplastic having anintegral skin.

FIG. 2 is an isometric view of a food package having features forease-of-use and for maintaining food quality.

FIG. 3 is a cross-sectional view of the food package of FIG. 2.

FIG. 4 is an isometric view of a rectangular food package.

FIG. 5 is an isometric view of another food package.

FIG. 6 is a block diagram showing details of consumer use of a foodpackage made according to the process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is packaging for food products made from foamedpolyethylene terepthalate (PET) or easily crystallized gradepolyethylene terepthalate (C-PET). PET and C-PET have advantageous foodcontact properties in that they do not release unscrubbed monomers suchas styrene or residual solvents into the food. Solid skins enhance theaesthetic appearance, sanitation, and abrasion resistance of thismaterial compared to competing foam surfaces.

Turning now to FIG. 1, illustrated is a sheet 102 of foamed polymermaterial. In the center of sheet 102 is foamed polymer 104 which maypossess a density of about 5% to about 99.9% of the density of unfoamedpolymer. Surfaces 106 a and 106 b, which may be substantially identicalto each other, are solid skins comprised of unfoamed polymer. Thethickness of each of skins 106 a and 106 b may vary from about 3% orless to about 25% or more of the total cross-sectional thickness and canbe determined by controlling values of certain manufacturing parametersas set forth below.

Two different processes are involved in the formation of skins onpolymeric materials foamed according to the present invention. First, ithas been discovered that when materials of semi-crystalline polymers,such as PET, polypropylene and syndiotactic polystyrene, are held underpressure of a plasticizing gas, they tend to crystallize over time, thecrystallization proceeding inward from the exposed surface of thepolymeric material. Therefore, in such gas-impregnated polymericmaterials held under pressure, there is a gradient of crystallinity thatdeclines from the surface to the interior of the material.

Associated with each semi-crystalline polymer is a threshold value forpercentage of crystallinity, which, if exceeded, results in materialthat, even though gas-impregnated, foams at a much higher temperaturethan the same polymer at lower percentages of crystallinity, if indeedsuch crystalline gas-impregnated material will foam at all. For PET, forexample, the threshold percentage is about 19% crystallinity. As thesesemi-crystalline polymeric materials are held under plasticizing gaspressure and their crystallinity increases over time from the surfaceinward, and as the percent crystallinity along the crystallinitygradient of the material increases above this threshold value, the depthof material that will not foam increases. On decompression and optionalheating as taught by the present invention, the inner portion of thematerial that is below the threshold value will foam, while the surfaceportion of the material that is above the threshold crystallinity valuewill remain unfoamed, thereby forming a skin of unfoamed polymer havinga higher crystallinity than the interior, foamed polymer.

In forming a highly crystallized skin on the foamed polymer according tothe foregoing, referring back to FIG. 1, surfaces 106 a and 106 b wouldcorrespond to portions of the polymeric material that had beencrystallized above the threshold value, while foamed inner section 104corresponds to a portion of the material whose crystallinity is belowthe threshold value. The highly crystallized skin possesses attributesgenerally associated with higher crystallinity in such polymers, such asimproved heat resistance, shape stability at high temperature, andstrength. The skin so produced is of the same exact material chemistryas the original polymer.

A second process enabling formation of skins on polymeric materialsfoamed according to the present invention is a result of the fact thatthe solvated gas desorbs from the polymer surface after decompression.If polymer subsequent to gas impregnation is allowed to desorb a portionof the solvated gas prior to bubble nucleation and formation, when thepolymer is finally foamed, it will possess an integral skin of thicknessproportional to the amount of solvated gas that was desorbed.

Such skins can be formed because solvated gas desorbs from the materialat its surface, with desorption resulting in a declining gradient ofsolvated gas concentration in the polymer material closer to the surfaceof the sheet. As the solvated gas concentration drops in the localizedmaterial at the surface, the surface of the polymer sheet to a certaindepth is no longer nascent foam and remains unfoamed material duringsubsequent processing, thereby forming an integral skin. Referring againto FIG. 1, for materials in which skins are formed by this process, 106a and 106 b would correspond to areas of the polymer where the solvatedgas had desorbed after decompression to the point where the area did notcontain sufficient solvated gas to foam, while foamed area 104 wouldcorrespond to the interior of the polymeric material where sufficientgas had remained solvated to cause foaming. The depth of this skindepends upon the amount of desorption that has taken place prior tofoaming, and therefore is dependent upon temperature, overall pressure,partial gas pressure, and time allowed for the decompressed impregnatedpolymer to desorb gas prior to foaming. The polymer in skins formed bythis second process need not have a level of crystallinity that isappreciably higher than that of the polymer in the foam beneath it. Theskin so produced is of the same exact material chemistry as the originalpolymer.

By controlling variables related to these two processes for skinformation, both the depth and the crystallinity of integral skin formedin polymers foamed according to the present invention may be controlled,whereby the attribute conferred to the material by the skin, such asheat resistance, high temperature shape stability, gas impermeability,stain resistance, enhanced appearance and so on, may be optimized whilethe material overall possesses the positive attributes of foam. Bybalancing the thickness of highly crystallized, heat stable skin againstthe amount of lower crystallinity higher ductility core, containers maybe fabricated which optimize these advantageous properties.

FIG. 2 is an isometric view of a food package 201 formed by the GITprocess. FIG. 3 is a cross sectional view of the box in FIG. 2 along avertical plane through its mid-line. These figures represent a pizzacontainer. Turning to FIG. 2, bottom 202 may be optionally joined to top204 via a living hinge 206. Alternatively, the pieces may be formedseparately. In a preferred embodiment, the bottom 202 or both top andbottom 204 and 202 of pizza container 201 are formed foam or partiallyfoamed material fabricated according to the GIT process. Pizza container201 may include one or more handles 208, indicated as separate handles208 a and 208 b, to make it easier to handle a container with hotcontents. Bumps, protrusions, or ridges 210, which may be embodied asother equivalent features, may be formed on the inside floor of thecontainer to keep the crust of the pizza substantially away from thebottom of the container. These features can help enhance the crispnessof the crust and also provide a place for excess oil to drain. Pizzacontainer 201 may be formed as a round or ovoid shape or as a square orrectangle. A round container is especially attractive due to itsimproved aesthetics and is economically feasible to produce despite thefact that such a shape generates considerable trim waste, owing to therecycleability of the trim material.

Turning now to FIG. 3, wherein is depicted pizza box 301 comprised ofbottom 302 connected to top 304 via live hinge 306 with optional handles308 a and 308 b, the pizza box may have an optional inner tray 312 thatacts as a baking, cutting, and/or serving tray. The tray may be shapedsubstantially the same as the outer box, having one or more handles 314to ease removal and handling. The outer box may be formed of relativelylow density foam, while the inner tray is formed of relatively highdensity foam having a higher crystallinity. To facilitate cutting, thetray may be made at a higher density or with a thicker unfoamed integralskin (as explained in U.S. Pat. No. 5,684,055) than required for thebox. Higher crystallinity of the inner tray imparts higher temperaturestability and allows it to act as a baking sheet. The lower densityouter box enhances thermal insulation during transport. In preferredembodiments, the foam has a density of 5 to 50% relative to unfoamed PET(the density of unfoamed PET being about 1.31 gm/cc). In especiallypreferred embodiments, the box has a relative density of 5-25%, whilethe tray's relative density ranges from 8%-35%. In preferred embodimentsof the pizza box and allied applications, the crystallinity level of thePET foam is 19-35%.

The inner tray 312 may be raised off the bottom of the outer box bybumps 310, for example, to further improve thermal isolation from theexterior. Alternatively, concave upward bumps may be formed in the trayitself or other features can be added, such as drain holes to allow oiland grease to seep away from the food into the bottom of the outer box.In a preferred embodiment, the upper surface of the inner tray 312 isrelatively flat and smooth to facilitate cutting.

The pizza box 201, 301 of FIGS. 2 and 3 may be delivered to or takenhome by the consumer with a cold or hot pizza inside. If hot, the hightemperature resistance of C-PET makes it possible for the consumer tocook the pizza right in the box without fear of melting it. Theinsulating characteristics of the foam material enhance maintenance ofserving temperature. The cut resistant integral skin makes the boxattractive for cutting the pizza directly thereon. It is alsoadvantageous to serve the pizza directly from the container. Thecracking resistance and wide thermal stability of the material make itpossible or desirable to refrigerate or freeze unconsumed leftoversdirectly in the same container. The high thermal stability of highlycrystallized PET makes it advantageous to reheat the pizza in amicrowave, convection, or conventional oven directly in the box.Finally, the entire package may be recycled, owing to the integralnature of the skins with their inherent chemical similarity to the corefoam, lack of flammable gases, and lack of chemical change to thepolymer during or required by the foaming process.

The round shape of the pizza box of FIGS. 2 and 3 is advantageous withrespect to heat retention. Insofar as heat retention is a function ofsurface area, a round box has 78.54% of the surface area of anequivalently dimensioned square box ( ). Therefore, a round pizza boxwill keep the pizza warmer longer.

The food container of FIGS. 2 and 3 is also amenable to other foodapplications such as take-and-bake cookie box with integral cookie sheetor other brown-and-serve applications.

Because of the substantially 100% recycleability of foam materialscreated according to the present process, round containers and othershapes that would normally be prohibitive due to the relatively largeamount of trim with ESF are especially feasible. This allows containersto be fabricated in shapes more optimized for the application, havingproperties such as improved aesthetics, improved heat retention, etc.

FIGS. 4 and 5 are isometric views of other embodiments of foodcontainers. FIGS. 4 and 5 include a closure comprising slot 402 and tabs404. The closures shown are functionality features and may be includedin the pizza box described in reference to FIGS. 2 and 3 above.. Thefood container 401 of FIG. 4 includes bottom 406 and top 408.Optionally, top 408 or a portion thereof may be left unfoamed, andtherefore transparent to maximize aesthetic qualities. This isaccomplished by not exposing that portion of the package to heat untilafter outgassing has been completed. Bottom 406 and optionally top 408may be foamed to maximize rigidity and insulating qualities.

FIG. 5 illustrates a circular food container. Circular container 501closes via slot 502 and tab 504 and comprises circular bottom 506 andtop 508. Such a shape is especially feasible with the present materialtechnology because of the substantially 100% recycleability of the wasteproduced by die cutting. It is a preferred embodiment because itsreduced surface area enhances thermal insulation qualities.

The containers of FIG. 2 through 5 are indicative of various aspects ofa broad variety of applications. For example, many restaurants have takeout boxes, the majority of which are made from polystyrene foam.Customers are offered the boxes to take home leftover portions of theirmeal. The polystyrene foam box easily tears, and cannot be put into theoven microwave to reheat. The present invention, when made from PET foamis durable, has superior insulation value to polystyrene, and food canbe reheated in the oven or microwave without removal from the box. Allor most of the steps necessary for preparation, storage, transport,eating, and storage of leftovers can be accomplished without removingthe food from the package.

Another application of the present invention is reusable orsemi-disposable PET foam food containers. The packages described hereare semi-disposable, but at a cost similar to that of single useconventional foam packages. They can be sealed with a matching foam lid,solid plastic lid, or cling film for storage, and can also be used forfood storage in the fridge or freezer and can be reused. A separateserving/cooking tray may be incorporated to fit inside the box and maybe of a higher density and toughness than the outside box to optimizethe inner tray for cutting.

Advantages of semi-disposable packages of the present invention comparedto existing heavier solid plastic containers, lighter thinner solidcontainers, or foamed plastic containers include:

-   -   1. Lower cost due to reduced material and the use of significant        recycled material content.    -   2. Higher rigidity even with less material used due to increased        wall thickness.    -   3. Increased insulation to keep hot foods hot and cold foods        cold longer for travel or “lunch box” use.    -   4. Increased versatility, with multi-use containers permitting        pre-cooking, freezing, cooking, serving, storage, reheating,        etc., owing to integral skin, use of high crystallinity pet foam        and internal tray.    -   5. Lower environmental cost of disposable packaging because up        to 100% recycled content may be used to create PET foam.    -   6. Greater service temperature range due to the choice of PET or        C-PET material.    -   7. Enhanced functionality: in some embodiments, the use of a        separate internal tray of higher density foam allows        preparation, cooking, cutting, and serving without the side of        the container interfering with the access to the food and with        enough strength to allow processing and eating steps; the outer        container is of lower density to add insulation and reduce        costs; and the tray is prevented from sliding within the box by        its handles and corresponding slots or notches in the box into        which the handles snap.

Because of the plasticizing effect of gas impregnation with plasticizinggas, it is possible to thermoform foamed containers according to thepresent invention having geometries unattainable in the prior art. Asdescribed above in relation to prior art thermoforming of polystyrenefoam, heretofore the limitations in such art restrict formed foamedcontainers to height to depth ratios to considerably less than 1:1, andwall angles to no less than about 40 deg from vertical. However,embodiments of the present invention practicing thermoforming ofmaterials plasticized by gas impregnation are not subject to theselimitations, enabling forming of articles with height to depth ratios of1.2 or greater and wall angles approaching vertical. While notillustrated, as will be clear to those of skill in the art thisinvention thereby advantageously permits thermoforming of many desirableobjects, such as foamed polymer cups, for example.

FIG. 6 is a block diagram illustrating use of the containers by theconsumer. As indicated, containers described herein may be used formultiple functions, including initial delivery 602 (with enhancedinsulation of hot or cold foods), serving 604, storage 606 (in arefrigerator or freezer, for example), reheating 608 and subsequent use604. Finally, because of the elimination in chemical alteration of thematerial during processes, as described in PCT application numberPCT/US__/______, titled MANUFACTURE OF FULLY RECYCLABLE FOAMED POLYMERFROM RECYCLED MATERIAL, filed contemporaneously herewith andincorporated herein by reference, the material may be recycled in itsentirety 610.

The utility of foamed objects is greatly enhanced when they arepartially crystallized. Such objects may possess service or operatingtemperatures as high as 200 deg. C. and therefore are well adapted tomany food preparation and service uses as well as other high temperatureapplications. By way of comparison, the maximum service temperature ofnon-crystalline PET (commonly called APET) is on the order of only 70deg. C.

Because of the high strength of the foam core, a high strength ofintegral skin, and selectively variable crystallinity, permitting deepdraw, hi-temperature resistance in highly crystallized polymers, andhigh impact strength when crystallinity is low, a very wide variety ofadvantageous packages may be created in the spirit of the presentinvention, of which the following are exemplary:

EXAMPLE 1

A pizza box used to sell frozen pizza.

EXAMPLE 2

Pizza boxes for “take and bake” pizza. The box is both used fortransport and for cooking food in a conventional oven.

EXAMPLE 3

Pizza boxes for cooked pizza right out of the oven and insulated duringthe trip home by the consumer. “Take out pizza”

EXAMPLE 4

“Brown and serve” rolls. Frozen rolls designed to be cooked frozen forimmediate serving.

EXAMPLE 5

Cookie dough frozen on cookie sheets to bake directly in the oven.

EXAMPLE 6

Hot fried chicken insulated while being taken home, then stored andreheated, etc. all in the same container.

EXAMPLE 7

Plastic foam butter or yogurt tubs pre-sterilized, filled and sealedunder sterile conditions. Wall angles nearly vertical and depth to widthover 1:1,

EXAMPLE 8

Hot drink cups, that insulate, are recyclable, are made form 0-100%recycled content, etc. Wall angles nearly vertical and depth to widthover 1:1

EXAMPLE 9

Non-food application such as steam or heat sterilizing in the packagebefore or after sealing or snap fastening a cover to reuse andre-sterilize.

CONCLUSIONS, RAMIFICATIONS, AND SCOPE

Accordingly, it can be seen that the invention described herein providesfoamed polymer articles made by an environmentally friendly process. Theversatility of the package is made possible by the inherent nature ofthe material. It insulates to keep hot food hot and cold food cold. Thepackage is advantageous over other disposable materials since itcontains no solvent residues or other undesirable chemicals that canspoil the taste, quality, or safety of the food. Crystallinity of thefoamed material may be selectively varied to balance high impactstrength with thermal resistance and formability

Although the detailed descriptions above contain many specifics, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of some of the presently preferredembodiments of this invention. Various other embodiments andramifications are possible within its scope, a number of which arediscussed in general terms above.

While the invention has been described with a certain degree ofparticularity, it should be recognized that elements thereof may bealtered by persons skilled in the art without departing from the spiritand scope of the invention. Accordingly, the present invention is notintended to be limited to the specific forms set forth herein, but onthe contrary, it is intended to cover such alternatives, modificationsand equivalents as can be reasonably included within the scope of theinvention. The invention is limited only by the claims appended heretoand their equivalents.

1. A container comprising material made by a solid state method for themanufacture of foamed polymeric material, comprising the steps: (a)interleaving an article of raw polymeric material with a gas channelingmeans; (b) exposing the interleaved article at elevated pressure to anon-reacting gas which is soluble in the polymer for a time sufficientto achieve a desired concentration of gas within the polymer, therebyforming an exposed polymeric article which is at least partiallygas-saturated; (c) decompressing the exposed polymeric article andseparating the article from the gas channeling means; (d) foaming theexposed article at a temperature below the melt temperature of thepolymeric material; and (e) trimming the foamed article to producefinished foamed polymeric material and scrap solid state process foamedpolymer, wherein the raw polymeric material comprises up to 100% of anyone of the group consisting of recycled pre-consumer polymer, recycledpost-consumer polymer and scrap solid state process foamed polymer. 2.The container of claim 1, wherein said container has a round base. 3.The container of claim 1, wherein said container has a substantiallyrectangular base.
 4. The container of claim 1, further comprising: (a) abottom member, (b) concave upward bumps affixed on horizontal plane ofsaid bottom member.
 5. The container of claim 1, further comprising: (a)a bottom piece, (b) a top piece, and (c) a living hinge connecting saidbottom piece to said top piece.
 6. The container of claim 5, furthercomprising at least one handle.
 7. The container of claim 5, furthercomprising a liner tray.
 8. A container comprising material by made by asolid state method for the manufacture of foamed polymeric material,comprising the steps: (a) interleaving an article of raw polymericmaterial with a gas channeling means; (b) exposing the interleavedarticle at elevated pressure to a non-reacting gas which is soluble inthe polymer for a time sufficient to achieve a desired concentration ofgas within the polymer, thereby forming an exposed polymeric articlewhich is at least partially gas-saturated; (c) decompressing the exposedpolymeric article and separating the article from the gas channelingmeans; (d) foaming the exposed article at a temperature below the melttemperature of the polymeric material; and (e) trimming the foamedarticle to produce finished foamed polymeric material and scrap solidstate process foamed polymer, wherein the foam has a relative density of5 to 80%.
 9. The container of claim 8, wherein said foam has an 8 to 35%relative density.
 10. The container of claim 8, wherein said containerhas a round base.
 11. The container of claim 8, wherein said containerhas a substantially rectangular base.
 12. The container of claim 8,further comprising: (a) a bottom member, (b) concave upward bumpsaffixed on horizontal plane of said bottom member.
 13. The container ofclaim 8, further comprising: (a) a bottom piece, (b) a top piece, and(c) a living hinge connecting said bottom piece to said top piece. 14.The container of claim 13, further comprising at least one handle. 15.The container of claim 13, further comprising a liner tray.
 16. Acontainer comprising material made by a solid state method for themanufacture of foamed polymeric material, comprising the steps: (a)interleaving an article of raw polymeric material with a gas channelingmeans; (b) exposing the interleaved article at elevated pressure to aplasticizing gas which is soluble in the polymer for a time sufficientto achieve a desired concentration of gas within the polymer, therebyforming an exposed polymeric article which is at least partiallygas-saturated; (c) decompressing the exposed polymeric article andseparating the article from the gas channeling means; (d) foaming theexposed article at a temperature below the melt temperature of thepolymeric material; and (e) trimming the foamed article to producefinished foamed polymeric material and scrap solid state process foamedpolymer, whereby the foamed polymer comprises PET crystallized to 19-35%at least on its surface.
 17. A container produced by a method ofthermoforming polymeric enabling deep draw and high definition,comprising the steps of: (a) interleaving an article of raw polymericmaterial with a gas channeling means; (b) exposing the interleavedarticle at elevated pressure to a plasticizing gas which is soluble inthe polymer for a time sufficient to achieve a desired concentration ofgas within the polymer, thereby forming an exposed polymeric articlewhich is at least partially gas-saturated; (c) decompressing the exposedpolymeric article and separating the article from the gas channelingmeans; and (d) thermoforming a container from the at least partiallygas-saturated polymeric article.
 18. A container produced by the methodaccording to claim 17, further comprising foaming the article prior tothermoforming.
 19. A container produced by the method according to claim18, wherein the article is foamed by achieving a suitable concentrationof gas within the polymer while exposing it and by heating the articleafter decompressing it to a temperature equal to or above the glasstransition temperature of the exposed article.
 20. A container producedby the method according to claim 19, wherein the temperature to whichthe article is heated after decompressing it is below the glasstransition temperature for the unexposed polymer.
 21. A containerproduced by the method according to claim 19, wherein the article isheated to a temperature equal to or above the glass transitiontemperature and below the melt temperature of the exposed article.
 22. Acontainer produced by the method according to claim 17, whereinthermoforming comprises heating the article to a temperature between itsglass transition temperature and its melting temperature.
 23. Acontainer produced by the method according to claim 22, wherein thethermoforming temperature is closer to the glass transition temperaturethan to the melting temperature of the raw polymeric material.
 24. Acontainer produced by the method according to claim 17, wherein thearticle is foamed when it is thermoformed.
 25. A container produced bythe method according to claim 17, wherein the article is thermoformedwithout heating.
 26. A container comprising an object produced by amethod of forming unfoamed polymeric objects enabling high definitionand deep draw, comprising: (a) interleaving an article of raw polymericmaterial with a gas channeling means; (b) exposing the interleavedarticle at elevated pressure to a plasticizing gas which is soluble inthe polymer for a time sufficient to achieve a desired concentration ofgas within the polymer, thereby forming an exposed polymeric articlewhich is at least partially gas-saturated; (c) separating the articlefrom the gas channeling means; (d) thermoforming the object from the atleast partially gas-saturated polymeric article while under pressure;and (e) decompressing the formed object and letting it desorb theplasticizing gas.
 27. A container produced by the method of claim 25,wherein the step of forming the object is performed without applyingadditional heat to the gas-saturated polymeric article.
 28. A containerproduced by the method of claim 26, wherein the article has two sidesand the object is formed by using pressure differences between the twosides of the article.
 29. A container produced by the method of claim26, wherein the object is formed using mechanical means.
 30. A containerproduced by the method of claim 26, wherein the object is formed usingpressure.
 31. A container produced by the method of claim 26, whereinthe object is formed using mechanical means to force the article intothe desired shape of the object.
 32. A container produced by the methodof claim 25, wherein the article comprises previously foamed polymer.33. A container of thermoformed foamed polymer having wall angles ofless than 35 degrees from vertical.
 34. A container of thermoformedfoamed polymer with a depth to width ratio exceeding 1:1.
 35. Athermoformed foamed polymer cup.
 36. A cup according to claim 34,further comprising a highly crystallized skin, whereby the cup is shapestable at temperatures exceeding 100 deg. C.
 37. A cup according toclaim 34, further comprising highly foamed crystallized PET throughout.38. A container comprising an object produced by a method of formingunfoamed polymeric material, comprising the steps: (a) interleaving anarticle of raw polymeric material with a gas channeling means; (b)exposing the interleaved article at elevated pressure to a plasticizinggas which is soluble in the polymer for a time sufficient to achieve adesired concentration of gas within the polymer, thereby forming anexposed polymeric article which is at least partially gas-saturated; (c)decompressing the exposed polymeric article and separating the articlefrom the gas channeling means; (d) foaming the exposed article at atemperature below the melt temperature of the polymeric material; (e)trimming the foamed article to produce finished foamed polymericmaterial and scrap solid state process foamed polymer; and (f) formingthe object, whereby the object comprises PET crystallized to 19-35%. 39.A container made from a sheet or roll of a thermoplastic material,wherein the thermoplastic material consists essentially of a virginthermoplastic material admixed with a previously processed thermoplasticmaterial, wherein the virgin material and the previously processedthermoplastic material are of the same chemical composition, and whereinthe previously processed thermoplastic material is in an amount thatranges from about 5% to about 95% by weight, the container being madefrom a process comprising at least the following steps: (a) pressurizingthe sheet or roll of the thermoplastic material with a plasticizing gasunder a selected pressure and period of time sufficient to yield areversibly plasticized thermoplastic material, the plasticizedthermoplastic material being impregnated with the plasticizing gas; (b)depressurizing the plasticized thermoplastic material to thereby desorbsome of the plasticizing gas from the plasticized thermoplasticmaterial; and (c) forming the plasticized thermoplastic material intothe container, wherein the step of forming occurs before the impregnatedplasticizing gas concentration falls below about 0.5 percent by weight.40. A container made from a sheet or roll of a thermoplastic material,the container being made from a process comprising at least thefollowing steps: (a) pressurizing the sheet or roll of the thermoplasticmaterial with a plasticizing gas under a selected pressure and period oftime sufficient to yield a reversibly plasticized thermoplasticmaterial, the plasticized thermoplastic material being impregnated withthe plasticizing gas; (b) depressurizing the plasticized thermoplasticmaterial to thereby desorb some of the plasticizing gas from theplasticized thermoplastic material; and (c) forming the plasticizedthermoplastic material into the container, wherein the step of formingoccurs before the impregnated plasticizing gas concentration falls belowabout 0.5 percent by weight of the plasticized thermoplastic material.41 A two-part polyethylene terephthalate (PET) container, comprising: anouter foamed polyethylene terephthalate (PET) container, wherein theouter container has a first integral skin and a first density, andwherein the first integral skin has a first surface weight percentcrystallinity; and an inner foamed polyethylene terephthalate (PET) traypositioned within the outer container, wherein the inner tray has asecond integral skin and a second density, and wherein the integral skinhas second surface weight percent crystallinity; and wherein the seconddensity and the second surface weight percent crystallinity of the innertray is greater than the first density and the first surface weightpercent crystallinity of the outer container.